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DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the demand defrost control (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 4.
TABLE 4
DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
DS1 and DS2 System Status, Fault and Lockout Codes
DS2
Green
DS1
Red
Type
Condition/Code
Possible Cause(s)
Solution
OFF
OFF
Status
Power problem
No power (24V) to demand defrost
control terminals R and C or demand
defrost control failure.
1.
Check control transformer power (24V).
2.
If power is available to demand defrost control and
trol.
Simultaneous SLOW
Flash
Status
Normal operation
Unit operating normally or in standby
mode.
None required.
Alternating SLOW
Flash
Status
5-minute anti-short cycle delay
Initial power up, safety trip, end of
room thermostat demand.
None required (jumper
TEST
pins to override)
Simultaneous FAST
Flash
Fault
Ambient Sensor Problem
Sensor being detected open or shorted or out of temperature range. Demand defrost control
will revert to time/temperature defrost operation. (System will still heat or cool).
Alternating
FAST Flash
Fault
Coil Sensor Problem
Sensor being detected open or shorted or out of temperature range. Demand defrost control
will not perform demand or time/temperature defrost operation. (System will still heat or cool.)
ON
ON
Fault
Demand Defrost Control Failure
Indicates that demand defrost control has internal component failure. Cycle 24VAC power to
demand defrost control. If code does not clear, replace demand defrost control.
OFF
SLOW
Flash
Fault
Low Pressure Fault
Restricted air flow over indoor or
outdoor coil.
Improper refrigerant charge in
system.
Improper metering device
installed or incorrect operation
of metering device.
Incorrect or improper sensor
location or connection to
system.
Remove any blockages or restrictions from coils
and/or fans. Check indoor and outdoor fan
motor for proper current draws.
Check system charge using subcooling
method.
Check system operating pressures and
compare to unit subcooling tables in this
instruction or located on unit access panel.
Make sure all pressure switches and sensors
have secure connections to system to prevent
refrigerant leaks or errors in pressure and
temperature measurements.
OFF
ON
Lockout
Low Pressure Lockout
SLOW
Flash
OFF
Fault
High Pressure Fault
ON
OFF
Lockout
High Pressure Lockout
SLOW
Flash
ON
Fault
Discharge Line Temperature Fault This code detects shorted sensor or high discharge temperatures. If the discharge line
temperature exceeds a temperature of 285ºF (140ºC) during compressor operation, the
demand defrost control will de-energize the compressor contactor output (and the defrost
output if active). The compressor will remain off until the discharge temperature has dropped
below 225ºF (107ºC).
sh
ON
Lockout
Discharge Line Temperature
Lockout
OFF
Fast
Flash
Fault
Discharge Sensor Fault
The demand defrost control detects open sensor or out of temperature sensor range. This fault
is detected by allowing the unit to run for 90 seconds before checking sensor resistance. If the
sensor resistance is not within range after 90 seconds, the demand defrost control will count
one fault. After 5 faults, the demand defrost control will lock out.
Fast
Flash
OFF
Lockout
Discharge Sensor Lockout
(Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
Field Operation Checklist for Two-Stage Modulation Compressors
Unit Readings
Y1 - First
‐
Stage
Expected results during Y2 demand
(Toggle switch On)
Y2 - Second
‐
Stage
Compressor
Voltage
Same
Amperage
Higher
Outdoor Unit Fan Motor
Amperage
Same or Higher
Temperature
Ambient
Same
Outdoor Coil Discharge Air
Higher
Compressor Discharge Line
Higher
Indoor Return Air
Same
Indoor Coil Discharge Air
Lower
Pressures
Suction (Vapor)
Lower
Liquid
Higher
